| With the increasing demand of industrial applications for microelectronics devices,high energy density devices and dynamic random access memory materials,the microelectronics industry has been committed to finding and preparing dielectric materials with strong reliability and long service life,colossal permittivity,high insulation resistivity and low dielectric loss.At present,in the field of rare earth amphoteric doped SrTiO3 colossal permittivity ceramics,researchers usually talk about the generation of colossal permittivity and resistance degradation are closely related to oxygen vacancy.However,the role of oxygen vacancy in ceramics,namely the generation,migration and annihilation of oxygen vacancy are rarely discussed.Therefore,this paper fully understands the oxygen vacancy and its associated defect state inside ceramics.The effect of oxygen vacancy diffusion behavior on the colossal permittivity,low dielectric loss and high insulation resistance of ceramics.The Sr1-xErxTiO3 ceramics were sintered in air with low dielectric loss and colossal permittivity,which were prepared by the traditional solid phase method by using amphoteric rare earth Er3+ions doped SrTiO3 ceramics.The relationship between permittivity and dielectric loss with frequency shows that when x=0.012,the colossal permittivity is 17790 at 1 kHz,and the permittivity is 14363 at 1 MHz,dielectric loss is 0.020 at 1 kHz.Defect dipoles and defect clusters are the main sources of colossal permittivity and low dielectric loss,which produce electron pinning effect,hinders the long-distance movement of electrons,and leads to the movement of electrons in the tiny region where the defect dipole is localized.On the one hand,the local polarization of electrons increases the dielectric constant.On the other hand,the long-range motion of electrons is inhibited,resulting in low dielectric loss.SrTiO3 ceramics with Er3+ ion doping content of x=0.012 were selected,and sintered in air,nitrogen,argon and hydrogen under four different oxygen partial pressures.Obtained more excellent performance of colossal permittivity,low dielectric loss ceramics,and by using variable temperature in-situ resistance monitoring equipment to explore an effective method to improve insulation resistivity.Ceramic sintered under hydrogen has colossal permittivity(132543@1kHz,157650@1MHz),ultra-low dielectric loss(0.009@1kHz,0.030@1MHz)and good frequency stability.The content of Ti3+and oxygen vacancy in this sample is significantly higher than that in the other three ceramic samples,because in a strong reducing atmosphere,oxygen vacancy is induced and Ti4+is more easily converted to Ti3+.At the same time,the existence of these defects and their coupling effect will promote the generation of defect dipoles and electronic pinning effect,so as to achieve colossal permittivity and ultra-low dielectric loss.In addition,the kinetics of oxygen vacancy diffusion and surface exchange during reoxidation at low,medium and high temperatures were also discussed.With the decrease of temperature,the resistivity oscillates and increases to 2.8×1014Ω·cm at 200℃.During this process,the diffusion rate of oxygen vacancy in the grain boundary is higher than that in the grain.With the decrease of external oxygen partial pressure,oxygen atoms move to the grain boundary first,thus filling the oxygen vacancy.Therefore,external oxygen partial pressure can be used to regulate the content of oxygen vacancy at the grain boundary,so that the insulation characteristics can be effectively regulated.Sr1-xErxTiO3 colossal permittivity ceramics with excellent comprehensive properties(colossal permittivity,low dielectric loss and high insulation resistivity)have been successfully prepared.Firstly,the ceramics sintered under nitrogen were annealed in air and oxygen respectively.Studies have shown that the ceramics annealed under air have better performance.Secondly,the ceramics sintered under hydrogen are annealed in air(abbreviated SET12-H-Air)and oxygen(abbreviated SET 12-H-O)respectively.SET 12-H-Air ceramics have higher permittivity(98095@1 kHz,102815@1 MHz),lower dielectric loss(0.008@1 kHz,0.010@1 MHz)and higher resistivity(13.2×1013Ω·cm),defect dipole[Ti’Ti-VO¨-Ti’Ti],[ErSr·-Ti’Ti],[2Er’Ti-VO¨]and[ErSr·-Er’Ti]to form in SET12-H-Air ceramics.The coupling effect of these dipoles results in low dielectric loss and colossal permittivity responses of SET 12-H-Air ceramics.In order to quantify the diffusion process of oxygen vacancy,the relaxation time τ(s)and diffusion coefficient D(cm2/s)of SET12-H and SET12-H-Air ceramics annealing in air and argon at different temperatures have been calculated.The diffusion of oxygen vacancy along the internal channel of ceramic is analyzed using Fick second law of one-dimensional carrier diffusion.Compared with the reoxidation and reduction processes,the order of magnitude of the diffusion coefficient at the same temperature is the same,indicating that the diffusion coefficient is strongly dependent on temperature.In the reoxidation stage,the diffusion coefficient increases first and then decreases with the decrease of temperature.When the temperature reaches 500℃,the diffusion coefficient is the highest,indicating that oxygen migrates along the diffusion channels of grain boundaries,grains,dislocations and surfaces at a very fast rate in the ceramics,filling up the large number of oxygen vacancies in the grain boundaries caused by the loss of oxygen in the strong reducing atmosphere. |
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